Method of manufacturing a plastic can body by injection molding a preform followed by a blow molding process

Abstract

A method of manufacturing a can body includes injection molding a preform including forming a bottom wall, a side wall, a curved shoulder and a flange extending outwardly from the shoulder. After molding, the preform is subjected to a stretch blow molding process to form the can body.

What is claimed is: 
     
       1. A method of manufacturing a cylindrical plastic can body, comprising: (a) injection-molding plastic to form a cylindrical plastic preform including:   forming a bottom and a side wall,   forming a molecularly oriented flange extending outwardly to a preset length from said side wall and having a thickness of one-third or less of the largest thickness of said side wall, said flange thickness being in the range from 0.3 mm to 0.7 mm so that said plastic molecularly orients as the plastic is injected to form said flange and the molecular orientation is in an amount sufficient for double-seaming said flange with a lid,   forming a curved shoulder having a preset radius for connecting said flange and said side wall; and   (b) biaxially stretch blow molding said cylindrical plastic preform to form a plastic can body.   
     
     
       2. A method according to claim 1, wherein said injection-molding step includes using a neck mold for defining said flange and an outer wall of an upper part of said shoulder, wherein the method further comprises the step of carrying said preform by said neck mold to a station at which said biaxially stretch blow molding step is preformed. 
     
     
       3. A method according to claim 2, wherein said injection-molding step includes using an injection cavity mold and a core mold. 
     
     
       4. A method according to claim 2, including providing said neck mold with a circular groove for defining an upper part and a lower part of a peripheral edge of said flange. 
     
     
       5. A method according to claim 1, wherein said shoulder forming step includes forming an upper portion of said shoulder with a thickness substantially equal to the thickness of the flange. 
     
     
       6. A method according to claim 1, wherein said shoulder forming step includes forming said shoulder with a tapered thickness. 
     
     
       7. A method of manufacturing a cylindrical plastic can body, comprising: a) injection-molding plastic to form a cylindrical plastic preform including:   forming a bottom and a side wall,   forming a molecularly oriented flange extending outwardly to a preset length from said side wall and having a thickness of one-third or less of the largest thickness of said side wall, said flange having a thickness in the range from 0.3 mm to 0.7 mm so that said plastic molecularly orients as the plastic is injected to form said flange and the molecular orientation is in an amount sufficient for double-seaming said flange with a lid,   forming a shoulder for connecting said flange and said side wall, said shoulder having a gradually reduced thickness toward an upper part of said shoulder; and   b) biaxially stretch blow molding said cylindrical plastic preform to form a plastic can body.   
     
     
       8. A method according to claim 7, wherein said injection-molding step includes using a neck mold for defining said flange and an outer wall of said upper part of said shoulder, wherein the method further comprises the step of carrying said preform by said neck mold to a station at which said biaxially stretch blow molding step is preformed. 
     
     
       9. A method according to claim 8, including providing said neck mold with a circular groove for defining an upper part and a lower part of a peripheral edge of said flange. 
     
     
       10. A method of manufacturing a cylindrical plastic can body, comprising: (a) injection-molding a cylindrical plastic preform including:   forming a bottom and a side wall,   forming a flange extending outwardly to a preset length from said side wall,   forming a curved shoulder having a preset radius for connecting said flange and said side wall; and   (b) biaxially stretch blow molding said cylindrical plastic preform to form a plastic can body, wherein said injection molding step includes using a first core mold for defining a first area of an inner wall of said preform and using a second core mold for defining a second area of said inner wall proximate to said first area, wherein said first area is larger than said second area, and the injection molding step further includes releasing said second core mold after releasing said first core mold but prior to changing the shape of the preform.